This disclosure relates to power supply control methods and apparatus. Specifically, the exemplary embodiments described herein provide methods and apparatus to control the output of a power supply operatively connected to a xerographic printing developer unit for transferring toner to a photoreceptor belt for subsequent transfer to a media sheet.
Generally, the process of electrophotographic printing includes charging a photoconductive member to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive surface is exposed to a light image from either a scanning laser beam, an LED source, or an original document being reproduced. This records an electrostatic latent image on the photoconductive surface. After the electrostatic latent image is recorded on the photoconductive surface, the latent image is developed. Two-component and single-component developer materials are commonly used for development. A typical two-component developer comprises magnetic carrier granules having toner particles adhering triboelectrically thereto. A single-component developer material typically comprises toner particles. Toner particles are attracted to the latent image, forming a toner powder image on the photoconductive surface. The toner powder image is subsequently transferred to a copy sheet. Finally, the toner powder image is heated to permanently fuse it to the copy sheet in image configuration.
The electrophotographic marking process given above can be modified to produce color images. One color electrophotographic marking process, called image-on-image (IOI) processing, superimposes toner powder images of different color toners onto the photoreceptor prior to the transfer of the composite toner powder image onto the substrate. While the IOI process provides certain benefits, such as a compact architecture, there are several challenges to its successful implementation. For instance, the viability of printing system concepts such as IOI processing requires development systems that do not interact with a previously toned image. Since several known development systems, such as conventional magnetic brush development and jumping single-component development, interact with the image on the receiver, a previously toned image will be scavenged by subsequent development if interacting development systems are used. Thus, for the IOI process, there is a need for scavengeless or non-interactive development systems.
Hybrid scavengeless development technology develops toner via a conventional magnetic brush onto the surface of a donor roll and a plurality of electrode wires are closely spaced from the toned donor roll in the development zone. An AC voltage is applied to the wires to generate a toner cloud in the development zone. This donor roll generally consists of a conductive core covered with a thin (50-200.mu.m) partially conductive layer. The magnetic brush roll is held at an electrical potential difference relative to the donor core to produce the field necessary for toner development. The toner layer on the donor roll is then disturbed by electric fields from a wire or set of wires to produce and sustain an agitated cloud of toner particles. Typical ac voltages of the wires relative to the donor are 600-900 Vpp at frequencies of 5-15 kHz. These ac signals are often square waves, rather than pure sinusoidal waves. Toner from the cloud is then developed onto the nearby photoreceptor by fields created by a latent image.
To produce the AC and DC voltages necessary to transfer toner from a cloud, high voltage power supplies (HVPS) can be controlled to change the output level according to an analog input control voltage. The voltage of this input represents the desired output level according to a specified relationship. In the circuits that are converting the analog control voltage to the high voltage output level there will be inaccuracies. These inaccuracies cause deviation in the above-mentioned relationship and are different for each source and each single HVPS. Therefore, it can be necessary to do adjustments on each such source and with each single HVPS produced. To enable the adjustments, usually trimmer potentiometers are used. The adjustment procedure with potentiometers, which is usually performed in production, is labor intensive and operator dependant.
There exists a need for HVPS methods and apparatus which minimize the cost and/or labor necessary to calibrate high voltage power supplies.